The invention relates to a diaphragm actuator of a control valve as specified in the preamble of claim 1.
Generic diaphragm actuators are known from U.S. Pat. No. 3,936,919, for example, and international patent WO 2008/112434 A1 in particular discloses a serial arrangement of springs in a diaphragm actuator. German patent document DE 10 2008 032 676 A1 discloses an expansion valve which has a gas permanently enclosed in a pressure chamber therein.
European patent document EP 2 028 377 A2 relates to a diaphragm actuator for actuating a control valve. This prior art diaphragm actuator comprises an actuator housing in which a diaphragm having a diaphragm disk is sealingly fitted in the actuator housing. A pressure chamber is thus formed, wherein application of pressure to the diaphragm will cause at least one spring which is provided therein and rests against the diaphragm disk and the actuator housing to be compressed, which diaphragm actuator is connected to a valve stem for actuating a valve body. It is also possible to have a plurality of springs arranged in parallel acting between the actuator housing and the connecting element.
Such arrangement is disadvantageous in that—if only one spring is connected in series—such spring may be prone to buckling if the valve stem travel is long. One measure to prevent the spring from buckling is to increase its outer diameter. However, this will have an adverse effect on the setting options of the spring parameters acting on the diaphragm disk.